The present invention relates to gasification and melting furnace and method for wastes wherein organic matters contained in municipal solid wastes and/or industrial solid wastes, which may be together referred to simply as xe2x80x9cwastesxe2x80x9d hereinafter, are gasified, then a gas (also referred to as xe2x80x9cenergy gasxe2x80x9d hereinafter) employable as fuel is recovered, low-boiling metals contained in the wastes are recovered as dust, and ash and valuable metals (also referred to simply as xe2x80x9cmetalsxe2x80x9d) contained in those wastes are recovered as molten slag and molten metals, respectively. Particularly, the invention is concerned with gasification and melting furnace and method permitting a stable operation over a long period.
As examples of wastes are included municipal refuses typical of which are garbages, plastic and iron scraps, shredder dusts of discarded automobiles and household appliances, bottom ash, and landfill wastes containing earth and sand.
In Japanese Patent Laid Open No. Hei 9-314100 there is disclosed a high-temperature reactor operating method for treating wastes.
The said high-temperature reactor operating method is characterized in that at least two oxygen lances are disposed below a wastes inlet in such a manner as to enhance the flow of molten waste and that at least two oxygen lances are disposed above the wastes inlet in such a manner as to obstruct the flow of rising gas components.
In the above publication, however, there is disclosed neither any concrete method nor any mode of embodiment about how to enhance the flow of molten waste and how to obstruct the flow of rising gas components.
The present inventors presume that introduced gases and gases resulting from decomposition of wastes form a rising flow to be discharged to the exterior of the system.
Thus, there is no such a downward flow as reinforces the flow of molten waste, but an upward flow is dominant. Likewise, there is no such flow as obstructs the flow of rising gas components, either. Therefore, it is difficult to artificially operate such a flow as obstructs the flow of rising gas components.
The present inventors think that the technique disclosed in the above publication is not clearly described and is based on principles contrary to the natural law and that therefore it is difficult to practice the said technique.
In Japanese Patent Laid Open No. Hei 10-148317 there are disclosed gasification and melting furnace and method wherein a series of steps comprising gasifying and melting wastes, dehydration and thermal decomposition, and reforming the resulting gas (indicating reforming up to CO, CO2, H2, and H2O) can be carried out in a single furnace without using the expensive coke and which can produce a clean energy gas not containing tar or dioxin. The gasification and melting furnace and method disclosed in the above publication is hereinafter referred to as the prior art.
The prior art relates to a gasification and melting technique for wastes using as a basic configuration a furnace which is provided at an upper portion thereof with both wastes inlet and gas outlet, also provided at a lower portion thereof with a molten slag/metal outlet, and further provided intermediate between the upper and lower portions with plural stages of tuyeres permitting a combustion sustaining gas and fuel to be independently blown off therethrough into the furnace. Further, as a development from the basic configuration the prior art is concerned with a gasification and melting technique for wastes which includes lances disposed in upper positions and capable of moving vertically toward the interior of the furnace and blowing off a combustion sustaining gas and fuel each independently, means for measuring the position of wastes introduced into the furnace, means for measuring the temperature of a middle portion, and means for measuring the temperature of an upper portion. This conventional technique is for separating wastes into an energy gas containing CO and H2 as main components, as well as molten slag and metals.
However, having tuyeres or lances for blowing off a combustion sustaining gas and fuel each independently give rise to problems such that at the time of blowing off fuel from a tuyere or a lance there is formed a low temperature region within the furnace due to an endothermic reaction induced by a thermal decomposition of hydrocarbons contained in the fuel, or in the case of a solid fuel the temperature is also reduced by a carrier gas used for blowing off the fuel. Even in the case where a solid or liquid fuel is not blown off into the furnace, it is necessary that a purge gas be allowed to flow constantly for preventing a fuel feed pipe from being clogged. Consequently, a low temperature region is formed in part of a fire spot and melting of slag and metal components contained in a thermal decomposition residue becomes unstable at an area below that low temperature region, thus making it impossible to effect a stable operation.
For preventing the occurrence of such a low temperature region it has so far been necessary to blow off not only fuel but also a combustion sustaining gas necessary for the combustion of the fuel. As a result, the amount of the combustion sustaining gas used per unit volume of wastes treated increases and the process efficiency is deteriorated.
It is an object of the present invention to provide a method and apparatus capable of preventing the occurrence of a low temperature region in a gasification and melting furnace, concentrating a fire spot for the combustion of wastes and thereby stably recovering molten slag and various metals, as well as an energy gas, which are high in added value.
Having repeated tests in a gasification and melting furnace, the prevent inventors became aware of the following points (A) to (E).
(A) As to a lance disposed at the center of the furnace, it is not only unnecessary but also detrimental to provide equipment for blowing off a combustion sustaining gas and fuel each independently.
Regarding LPG and LNG used as gas fuels and petroleum used as a liquid fuel, they themselves contain much hydrocarbons and hydrogen, so due to an endothermic reaction caused by thermal decomposition a low temperature region is formed in part of a fire spot even if a combustion sustaining gas is fed simultaneously with the introduction of fuel. Melting of slag and metal components contained in a thermal decomposition residue present below the fire spot becomes unstable due to the drop in temperature of the fire spot, with consequent formation of an unmelted portion or a re-solidified portion. Thus, a melting region is not formed stably and the flowing-down of melt becomes intermittent, resulting in that the furnace operation becomes unstable. When blowing off a solid fuel, it is necessary to use a carrier gas which is not combustion-sustainable, and this carrier gas strikes concentratively against an upper-end surface of wastes introduced into the furnace and promotes the cooling action, so that the furnace operation becomes still more unstable.
(B) Also as to an upper tuyere, like the furnace center lance, it is not necessary to blow off fuel because it is intended to reform and burn the gas resulting from thermal decomposition of the wastes.
(C) By disposing the furnace center lance along a central axis (also referred to as xe2x80x9cfurnace axisxe2x80x9d hereinafter) of the furnace it is made possible to melt the wastes concentratively at the central portion of the furnace and hence the furnace operation becomes extremely stable. Besides, by melting the wastes concentratively at a fire spot portion, a high temperature region is spaced apart from the furnace side wall and hence it is possible to prevent the furnace refractory from locally becoming high in temperature, so that the durability of the furnace refractory can be improved to a remarkable extent.
For melting the wastes concentratively at the central portion of the furnace it is important to control the position of an upper end surface of the wastes (also referred to as xe2x80x9cintroduced wastesxe2x80x9dhereinafter) introduced into the furnace. Particularly, for ensuring a stable operation it is important to measure the position of an upper end portion of the introduced wastes and control the upper end portion of the introduced wastes to a proper position.
In newly developing a device for measuring the position of an upper end face of the introduced wastes the present inventors became aware of the following points (a) to (c).
(a) Above the introduced waste, as a pipe is brought down while allowing a certain pressure of gas to be blown off from a lower end of the pipe, an upper end surface of the introduced wastes and the lower end of the pipe come into contact with each other, so that the lower end of the pipe is closed with the introduced wastes and the internal gas pressure of the pipe increases rapidly.
(b) If a relation between the distance of movement of the pipe and the position of the introduced wastes is determined in advance, the position of the introduced wastes can be determined from the distance of movement of the pipe at which distance there occurs an abrupt change in internal gas pressure of the pipe.
(c) Instead of the method wherein the lower end of the pipe is closed directly with the introduced wastes there can be adopted a method wherein the lower end of the pipe is closed indirectly with a top-shaped member attached to the pipe lower end and capable of freely moving vertically.
By the application of the above knowledges it is possible to easily measure the position of an upper end surface of the introduced wastes.
(D) As to an upper tuyere, by installing it so that the angle at which a combustion sustaining gas is blown off is displaced from the furnace axis direction, the flow of the combustion sustaining gas from the furnace center lance is not disturbed, so that a fire spot is formed stably at the same position and the effect of installation of the furnace center lance can be exhibited to the utmost extent. Additionally, the following effects can also be obtained.
Since the combustion sustaining gas from the upper tuyere does not directly strike against the furnace center lance, the refractory of the furnace center lance can be greatly improved in its durability.
By blowing off the combustion sustaining gas from the upper tuyere deviatedly from the furnace axis it is possible to let intra-furnace produced gas to circle and hence possible to accelerate mixing and the reforming reaction.
Dust contained in the gas is moved toward the furnace wall, thereby promoting the adhesion of dust to the furnace wall, the durability of the furnace can be improved remarkably by a self-coating action.
The amount of dust discharged from the gas outlet can be decreased, whereby the wastes treatment yield can be improved and the load on a dust remover can be diminished.
(E) By projecting a lower tuyere in the furnace axis direction, a combustion space formed by the lower tuyere and a melt flow-down zone from a fire spot formed by the furnace center lance can be brought into contact with each other. Thus, the effect of the above (c) can be exhibited to a greater extent.
The present invention has been accomplished on the basis of the above knowledges (A) to (E) and the gist thereof is as mentioned in the following (1) to (4). (1) A vertical gasification and melting furnace for wastes wherein wastes are burnt, organic matters contained in the wastes are gasified and recovered as an energy gas, and at the same time ash and metals contained in the wastes are recovered as melts, the furnace including a gas outlet, a molten slag/metal outlet, a wastes inlet, a furnace center lance, an upper tuyere, a lower tuyere, a position measuring device for measuring the position of an upper end surface of wastes introduced into the furnace, and an intra-furnace temperature measuring device, the gas outlet being formed in an upper portion of the furnace, the molten slag/metal outlet being formed in a lower portion of the furnace, the wastes inlet being formed in a position between the molten slag/metal outlet and the gas outlet, the furnace center lance being disposed in the upper portion of the furnace vertically movably along the axis of the furnace so as to blow off a combustion sustaining gas downward into the furnace, the upper tuyere being disposed at one or more stages in a furnace wall portion positioned between the wastes inlet and the gas outlet so that the angle at which the combustion sustaining gas is blown off is displaced from the furnace axis direction, and the lower tuyere being disposed at one or more stages in a furnace wall portion positioned between the wastes inlet and the molten slag/metal outlet and being projected into the furnace in a direction in which the combustion sustaining gas or both combustion sustaining gas and fuel blown off toward the furnace axis.
By using the above gasification and melting furnace for wastes (1) it is possible to prevent the occurrence of a low temperature region in the furnace and concentrate a fire spot for the combustion of wastes. As a result, molten slag and various metals, as well as an energy gas, which are high in added value, can be recovered stably.
(2) The above gasification and melting furnace wherein the position measuring device for measuring an upper end surface position of the wastes introduced into the furnace is provided with a pipe, a portion for blowing off a certain pressure of gas from a lower end of the pipe to the exterior of the pipe, a measuring instrument for measuring an internal pressure of the pipe, and a device for moving the pipe vertically.
By installing the above position measuring device (2) as the device for measuring an upper end surface position of the introduced wastes in the gasification and melting furnace (1), the accuracy in measuring an upper end surface position of the introduced wastes can be improved. As a result, molten slag and various metals, as well as an energy gas, which are high in added value, can be recovered in a more stable manner.
(3) A gasification and melting method for wastes using the above gasification and melting furnace (1), which method comprises introducing wastes into the furnace from the wastes inlet, allowing an upper end of the introduced wastes to be formed at a position above an upper end of a tuyere located at the top stage of the lower tuyeres and below a lower end of the wastes inlet, blowing off a combustion sustaining gas into the furnace from the furnace center lance and the upper tuyeres, blowing off a combustion sustaining gas or both combustion sustaining gas and fuel into the furnace from the lower tuyeres, allowing the introduced wastes to burn, holding the temperature of an upper end surface of the introduced wastes at 60xc2x0 C. or higher, holding the temperature of a fire spot at which a main flow of the combustion sustaining gas blown off from the furnace center lance strikes against the wastes"" surface, at 2000xc2x0 C. or higher, holding the gas present above the wastes inlet in the furnace at a temperature in the range of 1000xc2x0 C. to 1400xc2x0 C. and discharging it from the gas outlet, and discharging molten slag which contains molten inorganic oxides and metals, as well as molten metals, from the molten slag/metal outlet.
If the above gasification and melting method for wastes (3) is carried out using the above gasification and melting furnace (1), it is possible to stably recover molten slag and various metals, as well as an energy gas, which are high in added value.
(4) The above gasification and melting method (3) wherein control is made by vertical movement of the furnace center lance so that the diameter, df, of the fire spot formed by the furnace center lance and the inside diameter, D, of the furnace are in a relation of df/Dxe2x89xa60.6.
If the above gasification and melting method (4) is carried out in addition to the above method (3), the fire spot for burning the wastes can be further concentrated. As a result, molten slag and various metals, as well as an energy gas, which are high in added value, can be recovered more stably.